The present invention relates to a semiconductor memory device and a method of operating the same.
A memory cell in a semiconductor memory cell is programmed or erased through F-N tunneling. Electrons are charged in a floating gate according to a program operation, and the electrons charged in the floating gate are discharged to a substrate in accordance with on an erase operation. A threshold voltage of a memory cell depends on amount of the electrons charged in the floating gate. Data is determined according to level of a threshold voltage detected in a read operation.
To increase capacity of data stored in the semiconductor memory device, a memory cell includes a multi level cell storable data with multi levels corresponding to 2-bit or more information, unlike a common memory device. The semiconductor memory device may store data having various states by varying magnitude of the threshold voltage through adjusting the amount of the electrons charged in the floating gate of the multi level cell. Since a program method of the multi level cell increases innovatively capacity of a non-volatile memory cell, it has been widely used. In the program method of the multi level cell, two or more logical page data are programmed in one physical page.
However, according as plural logical pages are programmed in one physical page, period of time needed for the program operation increases and a program operation becomes complicate. Additionally, since width of threshold voltage distributions becomes narrow according as the number of target threshold voltage of memory cells augments, read margin may reduce, so it is difficult to read data. Also, interference phenomenon may occur between adjoining memory cells in the program operation.